Vascular intervention is today undertaken to treat a large number of diseases that had heretofore been treated by surgery. Stents are used widely in a number of applications to provide structural support to vessels that are being treated.
Stents are commonly used in the repair of aneurysms, as liners for vessels, or to provide mechanical support to prevent the collapse of stenosed or occluded vessels. Stents are typically delivered in a compressed state to a specific location inside the lumen of a vessel or other tubular structure, and then deployed at that location in the lumen to an expanded state. A stent has a diameter in its expanded state which is several times larger than the diameter of the stent in its compressed state. Stents are also frequently deployed in the treatment of atherosclerotic stenosis in blood vessels, especially after percutaneous transluminal coronary angioplasty (PTCA) procedures, to improve the results of the procedure and to reduce the likelihood of restenosis.
Stent designs are broadly divided into two categories, balloon expandable stents and self-expanding stents. The invention relates particularly to the delivery and positioning of self-expanding stents. The term self-expanding refers to the inherent material properties of the stent which cause the expansion of the stent once an external constraint has been removed. The effect is most commonly achieved by using a shape memory metallic alloy, such as nitinol.
Generally, stents are delivered to the desired location by means of a catheter, specifically referred to as a delivery catheter. Delivery catheters are threaded through a guiding catheter to the site of the disease and once the correct position has been established by means of fluoroscopic or other imaging method, the stent is deployed.
Delivery systems for self expanding stents generally comprise an inner component or core about which the stent is positioned in a retracted or reduced diameter and an outer sheath surrounding the stent. The stent is deployed by retracting the outer sheath relative to the inner component. This has the effect of removing the constraint on the stent which, on release, expands into an increased diameter deployed configuration. The procedure is controlled by a clinician by manipulating various components outside of the vasculature.
Conventional stent delivery systems suffer from the disadvantage that they are generally difficult to use to achieve accurate deployment of a stent at a desired site.
There is therefore a need for an improved deployment system which will address at least some of these problems.